Estimates of source range using horizontal multipath in continental shelf environments

Abstract

In a continental shelf environment, energy from an acoustic source propagating obliquely upslope repeatedly reflects from the sea surface and sloping seafloor with a consequent change in direction with each bottom reflection. Measurements of this type of effect can be observed in beamformed data from a horizontal line array. The arrivals from a single source are seen on two beams: a direct path with bearing angle corresponding to the source location and a refracted path with a bearing angle inshore of the source. In this work, the horizontal multipath effects are exploited to estimate the location of an acoustic source. Using the hybrid modeling approach of vertical modes and horizontal rays, rays are traced in the horizontal plane with refraction determined by the modal phase speed. Invoking reciprocity, the rays orientate from the center of the array and have launch angles equal to the estimated bearing angles of the direct and refracted paths. The location of the source in the horizontal plane is estimated from the point where the rays intersect. The technique is applied to data recorded on a horizontal line array located about 12 km east of the southern coast of Florida. [Work supported by ONR.]